Control voltage means in pulse receiver



Oct, 19, 1948. B. M. OLIVER CONTROL VOLTAGE MEANS IN PULSE RECEIVER 5 Sheets-Sheet 1 Filed Feb. 24, 1944 n.55 m .Surf MQ.

ATTORNEY OC- 19, 1948. B. Mouw-:R 2,451,632

CONTROL VOLTAGE MEANS IN PULSE RECEIVER Filed Feb. 24, 1944 5 Sheets-Sheet 2 RECEIVER /Nl/ENTOR B. M OUI/ER A TroRA/Ev Oct. 19, 1948. B. M. OLIVER CONTROL VOLTAGE MEANS IN PULSE RECEIVER 5 Sheets-Sheet 3 Filed Feb'. 24. 1944 A T TORNEV Oct. 19, 1948.

Filed Feb. 24, 1944 B, M. OLIVER 2,451,632

CONTROL VOLTAGE MEANSl IN PULSE RECEIVER 5 Sheets-Sheet 4 ANGLE OFROTAT/ON OF 08E SWITCHER, FROM A TRANSMITTER FIR/NG POINT /Nl/EN To@ B. M OUVER A T TQRNEK Oct. 19, 1948.

B. M. OLIVER CONTROL VOLTAGE MEANS IN PULSE RECEIVER Filed Feb. 24, 1944 VOL TAGE 5 Sheets-Sheet 54 rnANsM/rrE/J L /G' 8 PULSE R/-ggaA/s man 200 .4o EcE/ man@ oFsELEcrEa mns/sr A [gung/f VER rH/s sPAc//vc DEPENDE/vr C o/v RANGE u/v/rsE Trl/va 'Hl/200 20? RANGE u/v/r ouTPuT TRANsM/rrL-o Ig; PuLsE I I 200 krcur-of-FL/NE /v/c/e/o vou-AGE FIL-200 `[205 ,v2 smo VOLTAGE n T-cur-ol-FL/NE l.V200 @M206 lf2/LATE voLTAsE l rnA/vsM/rrsn 400 ARD POL/L55 p oL-LAY /NrERvAL l 1/ P /va smo voLmaE rk ED A/sM/rr 0a l P LsE 200 CUT-OFF LINE 1 l i- Awa/s MELE Y ry200 /vs cle/D VOLTAGE cur-oFFL/NEJ 20o u 0 212 {2l/20 l /vs PLATE VoLrlAcE RANGE No rcH 20/ '/voLTAGE AT CAN/00E 0F v6 a v7 LL m A Y CUT'WLNE SELECTED SIGNAL woEo s NoTcH s/c/vALs F 11,200 n 1'2/5 /AT ale/Ds oF vas v9 TME /N VEN TOR B. M. OL /VER ATTORNEY Patented Oct. 19, 1948 UNITED STATES ZSLBZ FFHCE CONTROL VOLTAGE MEANS IN PULSE RECEIVER Application February 24, 1944, Serial No. 523,722

(Cl. Z50- 20) 14 Claims.

This invention relates to electric wave modifying circuits and more particularly to wave modifying circuits of the type in which the low frequency modulation content in a signal wave comprising a multiplicity of short pulses of varying amplitude spaced by intervals longer than the duration of a pulse is increased.

Radio object locating and distance measuring systems (frequently called radar systems) are known in which radio frequency pulses of very short time duration (called transmitted pulses or emitted pulses) are emitted at intervals, reflections thereof are received from objects upon which the emitted pulses impinge and the reflection delay times for particular reflections are determined to provide indications of the distances of the object in which the respective reflected pulses are received. Radar systems of the type in which the beam of the antenna is continually moved so that its axis follows or tracks the target` are also known. In one such radar, la rotating wave guide scanner is turned about the axis of a paraboloidal reflector. The wave guide has an aperture which is displaced somewhat to one side of the axis so that as the scanner rotates around the axis of the reflector, the axis of the radio beam describes a cone in space. When the axis of the reflector is pointed directly at a target in space, the radio beam does not point squarely at the target and hence strikes it with somewhat less than maximum intensity. However, since the radio beam is describing a cone in space about the reector axis, it continues to project substantially the same amount of power toward the target at all positions in the scanning cycle. On the other hand, if the target moves oiT the reflector the beam at one part of its scan points more directly at the target while in the diametrically opposite part of its scan the beam points farther away from the target. In such a situation the echo pulses produced, each representative of the selected target, vary in amplitude at the frequency of rotation of the rotating antenna. The motor turning the antenna scanner at a low frequency, such as for example, 60 cycles, is known as the lobing motor and this low frequency rotation is known as the lobing frequency. The modulation content of the wave at the lobing frequency is a measure of the amount of angular displacement between the antenna axis and a direct line from the antenna to the target and can be utilized to produce two signals to move the lantenna through horizontal and vertical angles until the antenna axis and the line of sight to the target coincide. However,

due to the fact that the signal wave comprising successive echoes from the same target comprises a multiplicity of pulses of comparatively narrow width separated by periods of much greater duration during which no signal is received, the modulation component at the lobing frequency is very small. In a typical radar, 480 radio frequency pulses (called the transmitted pulses or emitted pulses) are emitted each second, and each transmitted or emitted pulse has a duration of .about one microsecond. Because in this typical case the pulse separation is about 2000 times the pulse duration, and also because the amount of pulse amplitude modulation at lobing frequency is very small (usually not more than 5 per cent) when the antenna is off target by the maximum permissible amount, it can be seen that most of the frequency components which account for the amplitude of the wave produced by the echoes from a particular target consist of the pulse repetition frequency and its high harmonics with small side frequencies while the component at the lobing frequency itself is very small. For example, if the pulse amplitude somewhere in the above radar system were 50 volts modulated 5 per cent, the video signal component at lobing frequency would be less than about 1 millivolt.l To amplify this component up to the required amplitude of several volts without system overload, it is necessary to filter out all components of a frequency greater than the lobing frequency. This is very difficult to accomplish without excessive phase shift at the lobing frequency.

It is an object of this invention to provide a novel Wave transforming circuit.

It is another object of this invention to provide means for transforming a wave comprising a series of relatively short pulses of substantially similar total energy spaced by time periods which are longer than the duration of any of the pulses and the amplitudes of which vary at a low frequency, into a wave in which the low frequency modulation content is greatly increased.

It is another object of this invention to providev means for satisfactorily extracting from a wave of relatively short pulses spaced apart by time periods greater than the duration of any pulse and amplitude modulated at .a relatively low frequency the modulation component at this low frequency.

In accordance with the specic embodiment of this invention, chosen by way of example for purposes of illustration, there is disclosed a wave transforming circuit which for convenience has been called a "lobing detector inasmuch as it detects or makes usable the modulation component of a wave comprising a plurality of relatively short pulses spaced apart by relatively long time intervals, said pulses being modulated at the lobing frequency. In a specific form of the invention, the lobing detector comprises a condenser charged to a fixed potential shortly before the reception of a selected video pulse and which is partially discharged a few microseconds later by the received selected video echoI signal from the target being tracked. The discharge of the condenser is thus caused to vary in amount in accordance with the modulation of the lobing frequency. This lobing frequency component of the condenser Voltage is the desired signal that is used to operate the angle tracking system to vary the position of the antenna axis so that it is on target in both elevation and azimuth, or, in other words, so that the error angle in azimuth (horizontal angle) and elevation (vertical angle) is reduced to substantially zero.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof in which:

Fig. 1 is a schematic block diagram of a radar system employing a wave transformer or lobing detector in accordance kwith the invention;

Fig. 2 is a circuit diagram of the wave transformer or lobing detector;

Fig. 3 is a circuit diagram of the signal selector used in the system of Fig. 1;

Fig. 4 is a circuit diagram of the delay circuit and pulse generator used in the system of Fig. 1;

Fig. 5 shows a modification of the lobing detector of Fig. 2; and

Figs. 6, 7 and 8 are diagrammatical and graphical representations to aid in understanding the invention.

Referring more particularly to the drawings, Fig. 1 shows, by way of example for illustrative purposes, an automatic tracking radar system in the three coordinates of range (slant distance to the target from the observing station), azimuth (horizontal angle between a reference direction and the vertical plane containing the line of sight to the target) and elevation (the vertical angle between the horizontal plane and the line of sight to the target). Fig. 1 is a single line block diagram to show the relationship of the various major elements of the system and is not intended to be a circuit diagram. It is to be understood that only elements necessary to show theoperation of the wave transforming circuit or lobing detector of this invention have been shown and that various. elements of an automatic tracking radar system in three coordinates, such as, for example, the oscilloscope and details of the range detector unit, have not been shown inasmuch as they are not necessary to explain the action of the lobing detector.

In the arrangement of Fig. 1, an ultra-high frequency pulse modulated wave is produced in a transmitterv ID. The transmitter may comprise, for example, a high voltage rectifier of any suitable form which supplies about 12,000 volts to a suitable charging circuit or element capable of producing a still higher voltage. After the charging voltage builds up to about 21,000 volts, any suitable rotary spark gap discharges the capacitor in the charging circuit. This discharge takes place in about one microsecond and causes the magnetron oscillator in the transmitter to oscil-l late for this brief period and send short pulses.

of radio frequency energy through a T-R box II to the antenna system I 2. A suitable antenna system is disclosed in an application by A. P. King, Serial No. 499,450, filed August 21, 1943, and in a corresponding British Patent 586,689, complete accepted March 27, 1947.

The antenna arrangement may, for example, comprise an open-ended circular antenna wave guide i3, the longitudinal axis of which is angu larly related to the principal axis of the paraboloidal reflector I4. The aperture at the open end of the guide is in the focal plane of the reector and placed a small distance to the side of the reflector axis. The antenna guide is connected to the T-R box by means of a stationary main transmission guide extending perpendicularly to the reflector axis and ultra-high frequency pulse modulated Waves are supplied to and collected fromv the guide. Means (not shown in Fig. 1) are provided for rotating the axis of the short wave guide about the refiector axis, and therefore for rotating the center of the aperture about the reflector focus, whereby the axis of the maximum directive lobe describes in space a cone of substantially circular cross-section, and lobe nutation is secured without moving the reflector i4. Means are also provided for moving the arrangement for the purpose of aligning the reflector axis, which coincides with the axis of the directive cone, with any direction in space. This means comprises, by Way of example, an azimuth motor IV for varying the horizontal angle between the reflector axis and the line between the antenna and the target and an elevation motor for varying the vertical angle between the reflector axis and the line between the antenna and the selected target it is desired to follow or track. The operation of the azimuth and elevation motors I5 and IG is controlled by signals from an angle tracking unit It to be described below. Mounted so as to rotate with the antenna scanner I3 are two low frequency generators represented by the boxes I8 and I8-A. These two generators, which are called the lobing generators, generate sinusoidal waves at the lobing frequency, that is, the frequency of rotation of the wave guide antenna i3 and which are degrees apart in phase. These waves are applied to the respective azimuth and elevation phase detectors 30 and 3E in the angle tracking unit i7 and are used as reference Waves.

Radio frequency pulses emitted by the antenna I3 and reiiected by the reflector S4 strike one or more objects and produce reiiections or echoes therefrom which are received by the same antenna system and transmitted through the T-R box ll to the receiver I9. The T-R box may be of any desirable type, for example, that employing a Western Electric Company 70S-A tube in a resonant cavity. This tube is filled with an ionizable gas and has a small gap therein. During reception, with the low voltages of the received energy, the gas is not ionized, the cavity is tuned to resonance and the received energy is applied to the receiver I9. During the transmission ofy a pulse from the transmitter ill, the voltages due to the pulse ionize the gas, thus detuning the cavity and substantially preventing most of the energy of the pulse from reaching the receiver I9.

In the receiver I9, the received waves are heterodyned to a convenient intermediate frequency and these intermediate frequency waves are amplified, detected, and applied to the signal selector 20 a circuit diagram of which is shown in Fig. 3.

Pulse energy from the transmitter I0, in the nature of a synchronizing pulse, controls the range unit 2| which is essentially a variable delay circuit or unit and produces a pulse 202 (see Fig. 8-B) of predetermined length a controllable period of time after the initiation of the pulse from the transmitter l0. A suitable range unit is disclosed in an application of L. A. Meacham, Serial No. 491,791, filed June 22, 1943 and which issued as Patent 2,422,204 on June 17, 1947. The output pulse from the circuit 2| is applied to a delay circuit and pulse generator 22 which, for example, produces a pulse 2|2 (see Fig. 8I) which has a duration corresponding to a range of, for example, 400 yards, the pulse starting after a time interval shown in Fig. 8-F, corresponding to a range of 400 yards from the start of the pulse in the range unit 2|. The unit 22 is shown in Fig. 4 and will be described more fully below. The output pulse from the range unit 2| is also applied to a range tracking unit 23 which is mechanically coupled (this connection being indicated by the dash line between the units 23 and 2|) to the range unit 2| to vary a condenser therein in such a Way as to vary the time each output pulse in the range unit is delayed from the corresponding unit pulse from the transmitter I0. Inasmuch as the present invention does not relate to automatic range tracking no details are given herein of the range tracking unit but reference is made to a copending application of B. M. Oliver, Serial No. 523,721, filed February 24, 1944, which shows, by way of example, an arrangement utilizing signals from a signal selector and pulses from a range unit to produce a voltage which drives a motor in one direction or the other to vary the delay period in the range unit in such a manner that the target is tracked in range.

The delay circuit shown in Fig. 4 produces a pulse, called a clearing-out pulse to be described more fully below, which is applied to the device shown in Fig. 2 and which, for convenience, will be designated the lobing detector. A selected portion of the video signal from the receiver is taken from the signal selector and applied to the input of the lobing detect-or as indicated in Fig. 2. This input (as shown in Fig. 6) comprises a plurality of relatively short echo pulses 20| (all from the same target) separated by relatively long intervals 220 of practically no signal energy. If the antenna is said to be on-target, that is, if its reflector axis passes through the target, al1 of the pulses 20| will be of substantially the same amplitude but if the antenna is not aimed directly at the target, the received pulses 20| from the selected target will be stronger in one position of the antenna than in another due to the fact that the lobe is highly directional. The pulses 20| will under these conditions have an envelope at the lobing frequency which, for example, is 60 cycles. For an arrangement wherein 480 pulses are transmitted per second and assuming that each transmitted pulse has a duration of about 1 microsecond there is a period of time 220 of approximately 2082 microseconds between successive video or echo signals lili from the selected target, that is, from the target being tracked or followed by the movement of the antenna reflector axis, It will be apparent from a consideration of Fig. 6 that the modulation content at the lobing frequency of 60 cycles is very small, being equal to the direct current component of the signal multiplied by the modulation index (per cent modulation divided by 100). Most of the frequency components which account for the amplitude of the pulse modulation exist as small side bands about the pulse frequency and its numerous high harmonics, the -component at the modulating frequency being by itself very small. The present invention in one of its more important aspects is concerned with the extraction from a pulse wave of the general type shown in Fig. 6, information as to variation in amplitude of the lobing frequency. The lobing detector 24V produces a substantially sinusoidal wave at the lobing frequency which is amplified by the amplier 25 and applied to both the azimuth phase detector 30 and the elevation phase detector 3| of the angle tracking unit i1. There signals are produced which are applied (through amplifiers 36 and 31, respectively) to the motors I5 and I6 to drive these motors in a direction to align the axis of the antenna with the line of sight to the selected target both in azimuth and elevation. Before going into a detailed description of how the output wave of the lobing detector 24 is produced and the manner in which it is utilized in the rest of the angle tracking unit |'l to control the azimuth and elevation motors |5 and I6, respectively, reference will be made to Figs. 2, 3 and 4 which are circuit diagrams of the elements 24, 20 and 22, respectively, represented by boxes in the system of Fig. 1.

Reference will rst be made to Fig. 4 which discloses a circuit 22 for producing a. pulse 2|2 (see Fig. 8 1) which has a duration corresponding to a range of 400 yards and the initiation of which is delayed by a period of time corresponding to a range of 400 yards after the initiation pulse from the range unit 2|. This circuit also produces the clearing out pulse 206 (see Fig 8-E) for the lobing detector 24. The circuit 22 comprises tubes VI, V2, V3, V4 and V5, the rst three of which make up the so-called delay circuit and the last two of which form the pulse generator for generating the delayed pulse 2|2 having a duration corresponding to 400 yards range. The function of the delay circuit comprising the tubes Vl, V2 and V3 is to produce a pulse 208.

The range unit output pulse, shown in Fig. 8-B as the pulse 202, is applied to the control element of the tube Vl through resistor 4|, a grid leak resistor 42 being connected in the circuit between the control element and ground. The cathode is connected directly to the suppressor grid and to ground through the parallel-connected resistor 43 and condenser d4 to apply bias to the grid. The cathode is placed at a positive potential with respect to ground by means of a voltage-dividing potentiometer comprising resistances 43, 45 `and |35 While the screen grid is placed at positive potential with respect t0 ground by means of the resistor 45 which is connected to the positive terminal of a source 4l of approximately 300 volts. The negative terminal of the source 4'! is connected to ground. The screen grid is also connected to ground through the condenser 52. The anode is connected to the positive terminal of the source LV! through resistor 49 and is connected to the control element of the tube V2 through condenser 50 and resistor 5|. Between the common terminal of the elements 5t and 5| and ground is a tuned circuit T comprising inductance member 52 and adjustable capacity member 53 of a few micromicrofarads. The cathode of the tube V2 is connected directly to ground and to the suppressor grid. The screen grid is connected through the resistance member 54 to the positive terminal of the source 4l and through the 7. condenser 55 to ground. The anode of the tube V2 is connected through the resistors 55 and 5'Tto the positive terminal of the source l?, the common terminal of resistances 56 and 51 being connected to ground through the condenser 58. The anode of the tube V2 is connected by means of a connection 59 to the lobing detector Z4 shown in Fig. 2 and through a condenser 55 and a resistance 6l to the control element of the tube V3, a resistor 52 being connected between the common terminal of the members 50 and 6=| and ground. The cathode of the tube V3 is connected directly to ground and to the suppressor grid while the screen grid is connected to the positive terminal of the source 47 through the resistor 63 and to ground through thel condenser 54A. The anode of the tube V3 is connected through the resistors 64 and 55 to the positive terminal of the source 4l, the common terminal of the members Gli and 55 being connected to ground through the condenser 55. The anode of the tube`V3 is also connected to the control element of the tube V4 through the condenser 61 and the resistance 60, the common terminal of the members 57 and 68 being conu nected toV ground through the leak resistor 55. The cathode of the tube V4 is connected directly to the suppressor grid and through the parallelconnected resistance member 'I0 and condenser 7| to ground. The cathode is placed at a positive potential with respect to ground by means of the voltage-dividing potentiometer between the positive terminal of the source 47 and ground comprising the resistances l0, 'H A and l2. The screen grid is placed at a positive potential by means of a connection to the positive terminal of the source 4l through the resistor l2 and is connectedv to ground through the condenser T3. The anode of the tube V4 is connected to the positive terminal of the source 4l through the resistor 'I4 and is connected to the control element of the tube V5 through condenser 'l5 and resistor 76, the common terminal of these last two members being connected to ground through the tuned circuit T comprising the paralleln connected inductance member 'il and the adjustable condenser 'I8 of only va few micromicrofarads. The cathode of the tube V5 is ydirectly connected to the suppressor grid and to ground. The screen grid is connected to the positive terminal of the source 47 through the resistor i9 and is connected to ground through the condenser 80. The anode of the tube V5 is connected to the positive terminal of the source 4'! through the resistors 8i and 82, the common terminal of these last two members being connected to ground through the condenser 83. The anode of the tube V5 is also connected through the coupling condenser 84 to the control element of the tube V6 in Fig. 3.

The operation of the circuit arrangement in Fig. 4 will now be described. The grid of the tube VI is biased below cut-01T because of the connection of the cathode to the positive terminal of the source 41 through the voltage divider cornprising the resistances 43, 45 and 46. When the pulse 202 is applied to the tube Vi, it conducts plate current for the instant that this grid is above the cut-off voltage. The cut-oir line 203 is shown in Fig. 8-C. The condenser 50 has been charged from the 30G-volt B supply through the resistor 49. When VI draws plate current during the pulse, condenser 53 is suddenly charged negatively through the path comprising condensers 44 and 50 and tube VI. The plate 8 voltage drop is about 200 volts and the grid of the tube V2 is driven negative by the same amount. The L-C network T begins an oscillation which is quenched after one-quarter cycle because the voltage across it begins to swing positive and the grid of the tube V2 begins to draw current. The oscillatory voltage has practically the same form as the pulse 204 shown in Fig. S-D which is the grid voltage curve of the tube V2. The cut-off line 205 for the tube V2 is also shown in this gure. The large negative grid voltage 204 applied to the grid of tube V2 cuts 01T this tube for a length of time equal to one-fourth of the period of one oscillation of the network T and produces a, plate voltage wave having the shape shown in Fig. 8-E. The sloping sides of this wave are caused by the condenser 60 and the total stray capacity of the lead 59 shunt ing the resistor 56 but do not interfere with the operation of the lobing detector circuit to which this wave is applied by means of the connection 59. The grid of the tube V3 is coupled to the plate of the tube V2 through the 10 micromicrofarad condenser 60. This condenser and the 270 ohrn resistance 52 have a very short time constant and differentiate the plate voltage wave produced on tube V2 to a form shown in Fig. 8-F, the pulse 257 in this figure being delayed from the pulse 252 by a time interval corresponding to substantially 400 yards range. The differentiated pulse 251 is amplified and changed in polarity by the tube V3 to produce a pulse 208 having the wave form shown in Fig. 8-G. This output is applied to the grid of the tube V4 which-is biased below cut-off by connecting its cathode to the B voltage supply 41 through the voltage divider arrangement comprising the resistances 10, 1 IA and '52. The positive pulse 208 applied to the control grid causes the plate voltage of this tube to drop suddenly (obviously the negative pulse 200 has no effect on the tube). Network T' starts to oscillate, but the oscillation stops at the end of one-quarter cycle when the grid of the tube V5 begins to swing positive and draw a, grid current. The operation of the tube V4 is similar to that of tube Vl except that its grid pulse has been delayed by the time of one-quarter cycle of an oscillation of the network T (corresponding to 400 yards range). The grid voltage wave 2|0 of the tube V5 is shown in Fig. 8-H. Tube V5 is cut oir by this large negative grid voltage and produces an output voltage pulse 2|2 similar to that shown in Fig. 8 1. This voltage is applied to the grid of the tube V6 in the signal selector circuit shown in Fig. 3. The length of the pulse 2l2 shown in Fig. 8-I corresponds to a range of approximately 400 yards and it starts after a time interval corresponding to a range of approximately 400 yards after the range unit pulse 202 shown in Fig. 8-B. The length of the pulse produced by the pulse generators V4 and V5 may be adjusted by means of the condenser 18.

Reference will now be made to Fig. 3 which shows tubes V6 and V1 and their associated circuit connections Which comprise a suitable signal selector 20. The output pulse 2i2 from the tube V5 of Fig. 4 is applied to the control grid of the tube V5 through the coupling condenser 84 and the resistor 85, the common terminal of these last two elements being connected to ground through the resistor 86. The cathode of the tube V6 is connected to ground through a resistor 3l' and is also directly connected to the suppressor grid. The anode and screen grid of the tube V6 are connected to the positive terminal of the source i1 through the resistor 38 and to ground through the resistor 09 which is shunted by a condenser 90. Tube V6 serves as a cathode follower, the output connection being made from the cathode of the tube V6 to the cathode of the tube V1. The video signal from the receiver 19, shown by Fig. 8-A and comprising for each transmitted pulse cycle a pulse 200 representative of a transmitted pulse and one or more pulses which are reflections or echoes from the targets (the pulse representing the target to be followed being designated by the reference ch-aracter 201) is applied to the control grid of the tube V1 through the coupling condenser 91 and the resistor 92. The common terminal of the members 91 and 92 is connected to ground through the resistor 96. The cathode of the tube V1 is connected to the suppressor grid thereof while the screen grid is connected to the positive terminal of the source 41 through the resistors 93 and 94, the common terminal of these two resistors being connected to ground through the condenser 95. The output from the signal selector 20 shown in Fig. 3 to the lobing detector of Fig. 2 is taken from the screen grid of the tube V1 through the connection 96. The anode of the tube V1 is connected to the positive terminal of the source 41 through resistors 91 and 98, the common terminal of these resistors being connected to ground through the condenser 99. The anode of the tube V1 is connected to an amplier 100, the output of which is applied to the range tracking unit 23. The manner in which such a selected signal is utilized for range tracking is described, by way of example, in the copending application of B. M. Oliver, Serial No. 523,721, led February 24, 1944.

The operation of the signal selector shown in Fig. 3 will now be described. This circuit, acting as a gate, permits only those signals which occur` within a certain small range (time) interval to be passed on to operate the automatic ranging equipment which includes the range tracking unit 23 and the lobing detector 24 the output of which is used for automatic angle tracking. In this process of selection, video signals from the receiver 19 represented in Fig. 8-A are combined with the 400 yard pulse 212 which is present in the output of the tube V5. The combination of these two is effected in the tube V1. The pedestal pulse 212 having a 400 yard width and a 400 yard delay behind the range pulse 202 obtained at the plate of the tube V is applied to the grid of the tube V5. The cathode -current and voltage across the cathode resistor 81 follow the Voltage applied to the grid of this tube. The positive potential across the resistor B1 is also applied to the cathode of the tube V1 since the resistor is common to both circuits. Ihis has the eiect of placing a more negative bias on the grid of the tube V1 during the application of positive pulses 212 to the grid of the tube V6. The incoming video signals from the receiver 19 are applied in the negative phase (as shown in Fig. 8-J) to the grid of the tube V1. Both the Video and pedestal pulses, therefore, cause a decrease in the plate current and a rise in the plate voltage of the tube V1. If the echo pulse corresponding tothe desired target occurs within the time span of the pulse 212, the two will be superposed as shown in Fig. 8-J, the echo 201 forming a notch in the pedestal pulse 214. In the operation of the range tracking unit 23, as described, for example, in the copending application of B. M. Oliver, Serial No. 523,721, led February 24, 1944, the range unit is controlled from the range tracking unit 23 in such a way that the output pulse from the range unit occurs at a time which will cause the pedestal pulse 214 to bracket the echo pulse 201 corresponding to the selected target. The output of the signal selector 20, which is applied to the tube V8 of the lobing detector 24 shown in Fig. 2 by means of the connection 96, the condenser 101 and the resistor 102, and to the control element of the tube V9 thereof through the elements 96, 101 and 103, is shown in Fig. S-K. A s shown in this figure, only those Video signals within the time span of pulses 212 pass through the signal selector. The tubes V8 and V9 are connected in parallel so as to amplify the signals applied to their control elements. The two cathodes are connected together and each is connected to ground through resistors 104 and 105 in series, the latter of which is adjustable. The condenser 106 is connected in parallel with the series-connected circuit comprising the elements 104 and 105. The anodes of the tubes V8 and V9 are connected together and through the anode-cathode path of the tube V10 to the positive terminal of the source 41. The cathodes of the tubes V8 and V9 are placed at a positive potential bymeans of the voltage divider comprising the resistors 105, 104 and 101. The cathode of the tube V10 is connected to ground through the condenser 108. The control element of the tube V10 is connected by means of the resistor 109 and the connection 59 to the anode of the tube V2 in the delay circuit shown in Fig. 4. The potential appearing across the condenser 10B is applied through resistance 110 to the control grid of the tube V11, this grid being connected to ground through the condenser 111. The cathode of the tube V11 is connected to ground through the resistor 1 12 and the anode of the tube V11 is connected directly to the positive terminal of the source 41. The lobing output wave is taken from across the resistance 112 through the coupling condenser 1 13.

The operation of the lobing detector will now be described. The lobing detector, as indicated in the system of Fig. 1, is part of the angle tracking unit 11. Its function is to extract the 60 cycle lobing frequency from the selected receiver video signal and pass this frequency to the rest of the angle tracking unit. Referring to Fig. 6, the pulses 201 Correspond to the pulses 201 in Fig. 8-K, there being one of these pulses for every transmitted pulse and thus they are approximately 2082 microseconds apart. There is no signal energy in the wave between the pulses 201. If the antenna 12 does not have its reflector axis aimed at the target, the pulses 201 will lie under a 60 cycle sinusoidal envelope, there being one complete cycle of the 60 cycle lobing frequency for every eight pulses, or in other words, for every complete rotation of the wave guide 13 eight pulses will be emitted. If the antenna axis is off-target the pulses emitted at some points of the rotation of the antenna will, because of the highly directional sensitivity of the antenna, produce a larger amplitude echo pulse 201 than others and the envelope 221 will be a sine wave the amplitude of which and the phase of which (With respect to the two reference waves generated by the 60 cycle generators 18 and 18-A) can be used to generate signals to center the antenna with respect to the target. Inasmuch as the wave of Fig. 6 has a low modulation content at the lobing frequency, the lobing detector is essentially a wave transformer as it produces an output wave, such as that shown in Fig. '7, which has a much larger modulation content at the lobing frequency.

Referring now to Fig. 2, the grid of the tube Vll is connected to the plate of the tube V2 in the 400 yard delay circuit, and the large positive plate Voltage pulse B, Fig. 8-E, carries the grid of VID positive, beginning with the start of the range unit pulse 202 and lasting for the 400 yard delay interval. The condenser w8 in the cathode circuit of the tube V|0 charges during the period that the grid of this tube is carried positive by the pulse 206. When the grid voltage decreases, the tube VIE! is cut olf and the condenser |68 remains charged. Theabove charging action occurs immediately after the range unit pulse 202. The selected signal shown above the cut-off line 2|5 in Fig. S-K and which is applied to the tubes V8 and V9 in parallel occurs after the range unit pulse 202 by a time equivalent to the 400 yard delay interval plus one-half the 400 yard range pulse 2|2, or 600 yards. It follows then that the condenser HBS will have been charged and left at its maximum potential (represented by the line 222 in Fig. 7) before the video signal is applied to the lobing detector by means of the connection 96. The cathode bias of the tubes V8 and V9 is adjusted so that the only signals on top of the 400 yard range pedestal 2H in Fig. 8-K cause the tubes V8 and V9 to conduct. Since the ungrounded side of the condenser |03 is connected to the plates of the tubes VS and V9, this condenser is partially discharged when the selected signal of Fig. S-K causes plate current to flow in VS and V9. The amount by which the condenser 28 is discharged is dependent upon the amount of plate current iiowing in the tubes V8 and V0 and therefore upon the amplitude of the signal pulse applied to the grids thereof. If the antenna is not pointing exactly at the target, the amplitude of the selected echo pulses 20| from the receiver will vary at the lobing frequency (as explained above in connection with Fig. 6) and the potential to which the condenser |08 is discharged will vary from pulse to pulse at this same rate. After the condenser |08 is partially discharged, it maintains this value of charge until it is again charged at the time of the next'range unit 202 pulse. The voltage on the condenser |08 will have a wave shape similar to that shown in Fig. 7, and will have a large lobing frequency component as indicated by the dotted line 2123 which is drawn through the mid-points of horizontal lines 224 representing the voltages to which condenser E08 is partially-discharged by the successive pulses. This component 223 has a time delay of about onehalf the interval between tWo successive transmitted pulses or l/Qeo of a second. This corresponds to a phase delay of about 221/2 degrees (with '-8 pulses per scan) which is compensated by shifting the phases of the reference Waves from the generators i8 and |8-A as will be pointed out below. The voltage across the condenser ll is applied through the resistor H0 to the grid of the tube Vl which operates as a cathode follower output tube. The low-pass lter action of the resistor H0 and the -condenser HI reduces the spikes 225 of the wave shown in Fig. 7 and a signal is produced (if the pointing error is large) like the typical signal 22B shown in Fig. l. This signal is amplified in any suitable amplier 25 and applied to the azimuth and elevation phase detectors and 3l.

The lobing detector 24 delivers to the .tw phase detectors 30 and 3| a constant voltage if the antenna is on-target or, if it is not ontarget, a 60-cycle voltage whose amplitude and phase indicates the antenna pointing error. If the antenna is pointed directly at a target, as pointed out above, all reected pulses will be of the same magnitude because the antenna beam, or lobe, will sweep around in a cone, the axis of which will pass through the target. Under this condition there will be no modulation of the video signal and a constant voltage onli7 will be delivered to the azimuth and elevation phase detectors 33 and 3|. If the antenna is not pointed directly at the target, stronger echoes will be received from lobes nearer the target than from those further away and since the speed of the lobe switching motor, that is, the motor (not shown) rotating the wave guide I3, is, for example, 3600 revolutions per minute, this results in a 60 cycle per second modulation of the reflected signal. It is the function of the rest of the angle tracking unit I1 to transform the 60 cycle lobing inputinto control voltages to drive the azimuth and elevation motors I5 and I6, thus changing the position ofthe antenna so that it will point directly at the selected target. Actually two control voltages are developed: one proportional to the antenna error in azimuth and one proportional to the antenna error in elevation. The amplitude and polarity of each control voltage denotes the magnitude and direction of the corresponding antenna pointing error.

As shown in the block diagram of Fig. 1, the modulated and amplified echo pulses are applied to the azimuth and elevation phase detectors 3D and 3|, respectively. Two 60 cycle voltages 22T and 22B, balanced with respect to ground and which are degrees out of phase with each other, are obtained from the two 60 cycle generators i8 and IB-A (if desired, the members i8 and iS--A can be a single two-phase generator) are used as reference waves for determining the instantaneous position of the antenna lobe. The azimuth reference wave 221 would normally have a maximum when the axis of the antenna beam is at its maximum horizontal displacement from the reector axis and the `elevation wave 228 would normally have a maximum when the axis of the antenna beam is at its maximum vertical displacement from the reiiector axis were it not for the phase shift produced by the lobing detector. Because of this phase shift, the phases of the reference waves are shifted accordingly to compensate for it. One voltage 221 is applied to the azimuth phase detector 30 by means of the connection |20 and the other reference voltage is applied to the elevation phase detector 3| by means of the connection |2| Each phase detector produces an output voltage which is proportional to the component in phase with its particular reference carrier wave. Any suitable phase detector may be utilized; for example, reference is made to the double tube arrangement in Patent 1,539,903, issued June 2, 1925 to L. M. Ilgenfritz for producing such a voltage component. The phase detector 30 comprises, for example, a double Vacuum tube circuit wherein the grids of both tubes are Varied in potential at a phase difference of degrees by means of the reference -wave 22'! while the wave 226 is applied to the grid-cathode circuit of both tubes in the same phase. If the phase displacement between 'Waves 226 and 221 is zero or 180 degrees (called the in-phase condition) a maximum signal is produced in the output circuit of the phase detector. A lobing signal 90 degrees or 270 degrees out of phase with the reference frequency wave 221 result-s in no signal voltage in the output circuit. If the phase of the lobing signal is between these two conditions, the output will be a signal voltage, the amplitude of which is somewhere between zero and the maximum obtained for the in-phase condition, depending on the phase diierence. The elevation phase detector 3| is similar to the device 30 except that the reference wave 228 is applied between the grids of the two tubes so that the voltages of the grids are 180 degrees apart instead of using the wave 221 in this manner as in the device 3|). The same lobing signal 226 is applied to both the azimuth and elevation phase detectors, but since the 60 cycle reference waves 221 and 228 for these two detectors are 90 degrees out of phase with each other, the resultant voltages Iwill change in different manners. For example, when the lobing frequency is in phase (or 180 degrees out of phase) with the azimuth reference wave 221, it will be 90 degrees out of phase with the elevation reference wave 223. This mea/ns that for this condition a signal voltage will be produced for controlling the azimuth circuit but no voltage will be produced in the elevation circuit. Obviously, for other conditions, signals representing errors in both azimuth and' elevation will be produced in the output circuits of the devices 3i) and 3 I.

The outputs of the phase detectors 3D and 3| after being amplied by the devices 32 and 33 are applied to the modulators 3d and 35, respectively, each of which may be, for example, of the copperoxide bridge type disclosed in Patent 2,025,158 issued December 24,1935 to F. A. Cowan. Also connected to each of these modulators is a 60- cycle carrier wave derived from the power line and a phase shifting network 36A connected to the source 38. With' no direct current input to each modulator, no (iO-cycle voltage appears in the modulator output. When a signal voltage is applied to the modulator 3A, for example, there appears at the modulator output a proportional GO-cycle voltage which either leads or lags the voltage of the source 38 by 90 degrees, depending on the polarity of the signal voltage. The outputs of the modulators 34 and 35 are applied to ampliers 36 and 31, respectively, and the outputs of these two ampliers are applied to the azimuth and elevation motors I and I6, respectively, to drive the antenna until it is on-target and thereby reduce the azimuth and elevation error voltages to zero.

Fig. 5 shows a modication of the arrangement shown in Fig. 2. In Fig. 5 portions to the left of the line X-X are intended to be the same as the portions to the left of the line X-X in Fig. 2 so they have not been reproduced in this gure. Moreover, in Fig. 5 all elements having th'e same reference characters as the corresponding elements in Fig. 2 are similar and operate in a similar manner. The arrangement of Fig. 5 differs from that of Fig. 2 in that the average potential of the heater for the cathodes in the tubes VIIJ and VII is made to follow the potential of the cathode of VIII. This is accomplished by means of the equal resistors |38 and |3I, the common terminal of which' is connected through resistor |32 to the cathode of the tube VII and through resistor |33 to ground. Resistors |32 and |33 serve as a rvoltage dividing potentiometer, their common terminal being at a potential less than the cathode of VII by an amount equal to the bias across that tube and hence at the potential of the grid of VII and the cathode of VIII. This prevents or greatly minimizes leakage between the cathode and heater of either of these tubes and especially VIII, thus preventing the charge of the condenser I 08 from leaking off during the interval between pulses and thereby producing an inaccurate output signal from the lobing detector.

Since the amount by which the condenser |08 is discharged each' cycle is proportional to the selected signal pulse strength, the average potential of this condenser and hence of the cathode of VII will be less, the greater the average selected signal strength. This variation in potential can be used to control automatically the receiver gain by well-known automatic gain control methods in such a manner as to hold the average selected signal strength substantially constant over a wide range of receiver input.

Th'e circuit constants of an operative form of the invention have been indicated on the ldrawing but it is to be understood that the invention is not limited to the use of these specic circuit constants as a change of one or more of the variables of the system may necessitate a change of the circuit constants in a manner understood by all those skilled in the art.

Although the present invention has been described in terms of various illustrative embodiments it should be realized that the invention and its several features are susceptible of embodiment in a wide variety of other forms. Hence the invention is to be understood as comprehending such other forms as may fairly come within the spirit and letter of the appended claims. For example, the wave transforming circuit designated the lobing detector is not limited to use in radar systems but may be used in any arrange-l ment wherein it is desired to produce a wave of the general form shown in Fig. 7 from a wave of the general type shown in Fig. 6. Moreover, while in the arrangements of Fig. 2 and Fig. 5, the condenser |08 is charged by the "clearing-out pulse and discharged by the incoming echo pulses, it is obvious that in a modification, the condenser |88 can be discharged to a reference potential and then charged by an amount depending on the amplitude of the echo pulse. In another modication, the clearing out pulse can be caused to return the condenser |08 to a potential which is not constant but rather varies in accordance with some modulation which it is desired to combine with the received signal. In the claims, the term reference level is intended to mean either a constant potential or one which varies :In a. desired manner.

Application Serial No. 583,472, filed March 19, 1945 contains claims relating to the system disclosed h'erein for keeping the axis of a rotating element aimed at an object.

What is claimed is:

l. In combination, means for forming a voltage wave comprising a plurality of short pulses which may be of varying amplitude spaced apart by time intervals which are long compared to the duration of a pulse, an energy storage element, means for conditioning said storage element by varying the amount of energy stored therein until the energy reaches a reference level before the occurrence of each pulse but af-ter the occurrence of the immediately preceding pulse, and means 15 for .applying each'pulse to the storage element to :vary the amount of ,energy stored therein by an amount depending on the amplitude .of that pulse.

2. The combination as in claim 1 in Which said reference level is a constant potential.

3. In combination, means for forming Va voltage wave comprising a plurality of short vpulses of varying amplitude spaced apart by time intervals which are long compared to the duration of a pulse, a condenser, means for conditioning said condenser by charging the energy therein .until it reaches a reference level before the occurrence of each pulse, and means for applying each pulse to the condenser to cause a partial discharge thereof by an amount depending on the amplitude of that pulse.

4. In combination, means for forming a voltage wave comprising a plurality of .short pulses of varying amplitude but of the same polarity spaced .apart by time intervals which arelong compared to the duration of Va pulse, said voltage Wave having a low frequency envelope, an energy storage element, means for conditioning said storage element by varying the amount of energy stored therein until the energy reaches a reference level before the occurrence of each pulse, and means for applying each pulse to the storage element to Vary the amount of energy stored -therein byk an amount depending .on the amplitude of that pulse.

5. A circuit arrangement for modifying a Voltage Wave which comprises ka plurality of short pulses of varying amplitude spaced apart by time intervals which are long compared to the dura- 4tion of a pulse to form a stepped voltage Wave, the potential of each step being determined by the amplitude ,of a corresponding pulse in the .input Wave, said circuit comprising an energy Astorage element, means for conditioning said storage element for varying the amount of energy ,stored therein until the energy Areaches a reference 'level before the occurrence of each pulse in ,the input wave, and means for applying each pulse to the storage element to vary the amount @of energy stored therein by an amount depending on the amplitude of that pulse, whereby there is formed across said storage element 'a stepped voltage Wave the time interval between adjacent steps being short compared to the duration of a step.

.6. A circuit arrangement for modifying a volt- ,v

.age input wave comprising a series of short pulses which comprises a condenser, means for conditioning said condenser by charging the energy .therein until it reaches a reference level before the occurrence of each pulse in the input Wave, and means for applying each pulse in the input wave to the condenser to partially discharge it by an amount depending on the amplitude of that pulse, whereby :there is formed'across said storage element a stepped voltage wave the time interval between adjacent steps being short compared to 4the duration of a step. Y

7. The combination of the circuit Aarrangement of claim 6 with a radio circuit, and means for utilizing said stepped voltage Wave to control the gain of signals in said radio cir-cuit.

8. In combination, a space current device comprising an anode, a cathode and a .control element, a condenser, means for connecting said condenser in circuit with the cathode of said space current device, means for applying to the cathode control element circuit of said device a voltage wave comprising a Vplurality of short' 7pulses of varying amplitude spaced apart by time lintervals which are long compared to the duration of a pulse, means for conditioning said cori--` denser by varying the amount of energy stored therein until the energy reaches a reference level efore the occurrence of each pulse, and means for applying each pulse to the condenser to Vary the amount of energy stored therein by an amount depending on the intensity of that pulse.

9. yIn combination, a rst space current device comprising an anode, a cathode and a control element, a second space current device comprising an anode, a cathode and a control element, a condenser, means for connecting said condenser in circuit with the cathode of said first space current device, means for applying to the cathode control element circuit of said rst device a voltage Wave comprising a plurality of short pulses of varying amplitude spaced apart by time intervals which are long compared to the duration of a pulse, means for conditioning said condenser by varying the amount of energy stored therein until the energy reaches a reference level before the occurrence of each pulse, means for applying the voltage variations across said condenser to the control kelement circuit of said second space current device, and means for obtaining an output wave from the cathode circuit of said second space current device.

l0. In combination, a rst space current device compran-ig an anode, a cathode and a :control element, a second space current device comprising an anode, a cathode and a control element, a condenser, means for connecting said condenser in circuit with the cathode of said first space .current device, means for applying to the cathode control element circuit of said rst device a voltage Wave comprising a plurality of short pulses of varying amplitude spaced apart by time intervals which are long compared to the duration of a pulse, means for conditioning said condenser by varying the amount of energy stored therein until the energy reaches a reference level before the occurrence of each pulse, and means for applying the voltage variations across saidV condenser to the cathode-control element circuit vof said second space current device, said last-mentioned means including a low-pass ilter circuit, and means for .obtaining an outputl Wave from the anode-cathode circuit of said second space current device.

1l. In combination, a rst space current device comprising an anode, a cathode and a control element, a second space current device comprising anode, a cathode and a control element, a condenser, means for connecting said condenser in circuit between the cathode and control :element of vsaid first space current device, means including said second discharge device Vfor applying .to the cathode-control element circuit of said rst device a voltage Wave comprising a plurality of short'pulses of varying amplitude spaced `apart by time intervals which are long compared to the duration of a pulse, means for conditioning said condenser by varying the amount of energy stored therein until the energy reaches a refer- .ence level before the occurrence of each pulse, -means for applying each pulse to the condenser to vary the amount of energy stored therein by .an amount depending on the intensity of that lpulse, a heater element for each of said cathodes, .and means for causing the potential of each of `said heaters to vary with the potential of -one 4of the cathodes.

l2. A 4circuit arrangement for modifying a voltage Wave which comprises a plurality of short pulses of varying amplitude spaced apart by time intervals which are long compared to the duration of a pulse to form a stepped voltage wave, the potential of each step being determined by the amplitude of a corresponding pulse in the input wave, said circuit arrangement comprising an energy storage element, means for applying each pulse to the storage element to Vary the amount of energy stored therein by an amount depending on the amplitude of that pulse, and means for thereafter Varying the amount of energy stored in said storage element until it reaches a reference level before the occurrence of the next pulse in the input Wave.

13. A circuit arrangement for modifying a voltage wave which comprises a plurality of short pulses of varying amplitude spaced apart by time intervals which are long compared to the duration of a pulse to form a stepped voltage Wave, the potential of each step being determined by the amplitude of a corresponding pulse in the input Wave, said circuit arrangement comprising an energy storage element, means for applying each pulse to the storage element to almost instantaneously vary the amount of energy stored therein by an amount depending on the amplitude of that pulse, and means for thereafter almost instantaneously varying the amount of energy stored in said storage element until it reaches a reference level before the occurrence of the next pulse in the input Wave.

18 14. A pulse generator comprising a condenser, a source of direct potential for :charging said condenser, means for repeatedly connecting said source to said condenser, a circuit for discharging said condenser after each charging thereof comprising a variable resistance, and means for utilizing each short voltage pulse of a series of such pulses which are widely spaced in time to impulsively vary said resistance from a high Value to a low value which is dependent upon the amplitude of the pulse.

BERNARD M. OLIVER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,004,294 Planck June 11, 1935 2,186,268 Pakala Jan. 9, 1940 2,221,452 Lewis Nov. 12, 1940 2,222,172 Dimmick Nov. 19, 1940 2,227,906 Kellogg Jan. 7, 1941 2,231,929 Lyman Feb. 18, 1941 2,266,194 Guanella Dec. 16, 1941 2,275,224 Henroteau Mar. 3, 1942 2,277,516 Henroteau Mar. 24, 1942 2,367,277 Henroteau Jan. 16, 1945 

